This invention is generally directed to toner and developer compositions. More specifically, the present invention is directed to a process for preparing colored toner compositions wherein each of the selected pigments are encapsulated with a continuous shell of a low molecular weight waxy compound, inclusive of polyethylene or polypropylene. Thus, in one embodiment of the present invention there is provided a toner composition encapsulated with a substantially continuous shell of a polyethylene or polypropylene wax of molecular weight of from about 1,000 to about 6,000, and comprised of resin particles, and colored pigment particles. The encapsulation enables the resulting toner compositions to possess substantially identical charging characteristics, and decreased aging over extended time periods. Accordingly, the toner and developer compositions of the present invention are useful in permitting the development of colored images in electrophotographic imaging and printing processes. Specifically, thus the toner compositions illustrated herein can be selected for use in generating colored images while retaining stable triboelectric electrical characteristics. Furthermore, in accordance with the present invention there are provided toner and developer compositions wherein each of the separate colored toner particles, inclusive of cyan, magenta, and yellow age at substantially the same rate permitting developed prints with the same color intensity beginning with the first printing or imaging cycle and continuing on for an extended number of cycles.
Toner and developer compositions with waxy materials are known. Thus, for example, there is described in British Pat. No. 1,442,835 a toner composition with a styrene homopolymer or copolymer resin, and at least one polyalkylene compound selected from polyethylene and polypropylene. According to the disclosure of this patent, reference page 2, beginning at line 90, the starting polymer resin may be either a homopolymer of styrene, or a copolymer of styrene with other ethylenically unsatured monomers, specific examples of which are disclosed on page 3, beginning at line 1. Polyalkylene compounds selected for incorporation into the toner compositions disclosed in this patent include polyethylenes and polypropylenes of an average molecular weight of from about 2,000 to about 6,000.
Additionally, there is disclosed in U.S. Pat. No. 4,460,672 a developer composition mixture comprised of electrostatic toner particles consisting of resin particles, pigment particles, a waxy material with a molecular weight of from about 500 to about 20,000; and further included in the composition from about 0.5 percent by weight to about 10 percent by weight of a charge enhancing additive selected from, for example, alkyl pyridinium halides, organic sulfonate compositions, and organic sulfate compositions. The disclosure of this patent is totally incorporated herein by reference.
Also, there is disclosed in U.S. Pat. No. 4,206,247 a developer composition with a mixture of resins including a low molecular weight polyolefin and alkyl modified phenol resins. More specifically, is it indicated in this patent, reference column 4, line 6, that the invention is directed to a process which comprises the steps of developing an image with toner particles containing in certain proportions at least one resin selected from group A, at least one resin selected from the group B resins, wherein the resins of group A include a low molecular weight polyethylene; a low molecular weight polypropylene; and similar materials; and wherein the group B resins include natural resin modified maleic acid resins, natural modified pentaerythritol resins, and other resins. As examples of group A resins there is mentioned polystyrene, styrene series copolymers, polyesters, epoxy resins, and the like, reference the disclosure in column 5, line 47. The molecular weight of the polypropylene, or polyethylene used is from about 1,000 to about 10,000, and preferably from about 1,000 to 5,000.
Furthermore, there is described in a copending application, U.S. Ser. No. 655,381, now U.S. Pat. No. 4,556,624, entitled Toner Compositions with Crosslinked Resins and Low Molecular Weight Wax, the disclosure of which is totally incorporated herein by reference, toner compositions comprised of crosslinked copolymer resins including styrene alkyl methacrylates crosslinked with, for example, divinylbenzene or a polyblend mixture of these crosslinked copolymer resins with a second polymer, including styrene butadiene copolymer resins; pigment particles; a low molecular weight waxy composition selected from the group consisting of polyethylene and polypropylene; and as optional components charge enhancing additives selected from the group consisting of alkyl pyridinium halides, and organic sulfonate compounds.
Other representative prior art includes U.S. Pat. Nos. 4,187,194 and 3,788,994, which disclose encapsulation processes wherein the liquid or pressure fixable toner particles selected may be protected by a low molecular weight polyethylene. Patents of background interest and located as a result of a patentability search include 4,206,247 and 4,418,137 wherein combinations of resins are selected for formulating toner compositions including low molecular weight polypropylenes; 4,002,776; 4,254,201; 4,262,076; 4,293,632; and 4,379,825. The aforementioned patents relate generally to encapsulation and/or the use of polypropylene in toner compositions.
Additionally, the Xerox Corporation 6500.RTM. copying machine selects separate toner compositions, inclusive of a magneta toner composition, a cyan toner composition, and a yellow toner composition. It is known that in some instances with the 6500.RTM. images of poor copy quality result. Thus, these images have undesirable background deposits, and low densities unless the bias on the developer mixtures is adjusted, resulting from different triboelectric charging properties as each of the colored toner compositions age. This problem is eliminated with the toner compositions of the present invention in that there can be achieved substantially similar stable triboelectric charging characteristics for the colored toner compositions primarily as a result of the presence of a shell of the low molecular weight waxy compound present on the surface of the toner pigment particles. Moreover, with the toner composition of the present invention it may be unnecessary to select toner particles of a different composition as is the situation with many of the prior art developers. Furthermore, only a limited number of useful colored pigments are available, therefore, substantial efforts have been consumed in affecting adjustments to the aforementioned colored toner compositions for enabling improved copy quality with extended usage.
Accordingly, there continues to be a need for toner compositions with improved electrical stability. There is also a need for colored toner compositions wherein each of the separate toners generated are of substantially equal triboelectric charging values. Further, there is a need for colored toner compositions wherein the resulting separate toners generated do not significantly age with an extended number of copy cycles. Additionally, there is a need for magenta, cyan, yellow; highlight colors such as red, blue, and green; toner compositions with similar triboelectric charging characteristics; and wherein these characteristics are maintained for an extended number of imaging cycles. There is also a need for colored toner compositions with improved stable electrical properties thereby enabling substantially similar color intensities for an extended number of imaging cycles.